The
Kepler space telescope was hobbled in May when the second of
its four orientation-maintaining reaction wheels failed, robbing
the instrument of its precision pointing ability. Engineers
managed to get the balky wheels turning again recently, but both
devices are far from healthy, showing much higher levels of
friction than they once did.

"It's not going to go back to its original mission; it's going to
be something less than that," said Kepler deputy project manager
Charlie Sobeck of NASA's Ames Research Center in Moffett Field,
Calif. "But how much less, and how much usefulness it'll have —
it's really still very much up in the air."

Spinning Kepler's wheels

Kepler launched in March 2009, kicking off a 3.5-year prime
mission to determine how common Earth-like
planets are throughout the Milky Way galaxy.

The observatory is designed to stare at more than 150,000 stars
simultaneously, looking for the telltale brightness dips caused
when planets pass in front of, or transit, these stars' faces.

Kepler needs three functioning gyroscope-like reaction wheels to
perform this precision work. It launched with four — three for
immediate use and one set aside as a spare. But one wheel, known
as number two, failed in July 2012. Then another (number four)
gave up the ghost on May 11 of this year,
halting Kepler's exoplanet search.

After the second failure, Kepler team members began devising ways
to potentially bring the two wheels back. They performed recovery
tests over the last week, commanding wheels four and two to spin
on July 18 and July 22, respectively.

Wheel four rotated in one direction (counterclockwise), while
wheel two spun in both directions, mission officials announced
Wednesday (July 24). This was a victory of sorts, but a qualified
one.

"Both wheels are showing substantially higher friction than a
good wheel would show," Sobeck told SPACE.com. Those friction
levels probably won't come down, he added, as the recovery team
has already tried a number of strategies to this effect.

"Just saying that we could go back to science and operate
normally, as we have — it's unlikely to happen," Sobeck said.
"The question then becomes, Can you drive a wheel with
substantial friction and still do science with it? We really
don't know the answer to that question, so that'll be the next
test that we run."

Sending astronauts out to service Kepler, as was done five
separate times with NASA's Hubble
Space Telescope, is not an option. Kepler orbits the sun
rather than Earth, and it's currently millions of miles from our
planet.

Putting Kepler back to work

The $600 million Kepler mission has revolutionized the search for
alien
planets, spotting 3,277 exoplanet candidates to date. Just
135 have been confirmed so far by follow-up observations, but
mission scientists expect that more than 90 percent will end up
being the real deal.

While Kepler is unlikely to resume the operations that detected
so many far-flung worlds, the spacecraft may still be able to
gather valuable exoplanet data.
For example, Kepler will probably be capable of precision
pointing for short periods of time, even in its current
condition, Sobeck said.

"We've got a lot of planetary candidates that we know when the
transits occur," he said. "We might be able to schedule a day or
two days of precise pointing during that period and catch the
next transit, and improve our knowledge of the planetary systems
— maybe determine the mass of those systems, things like that."

"So it's not clear that planet hunting per se is off the
table," he added. "It's just a different style of hunting."

In two or three weeks, the Kepler team aims to return the
observatory to wheel control, Sobeck said. The observatory's
handlers will attempt to point Kepler using its reaction wheels,
first coarsely and then, if that works, with much more precision.